1. Field of the Invention
This invention relates to a microscope, and particularly to a microscope which picks up the image of a specimen by a television camera and through which the image is observed.
2. Related Background Art
Usually, a microscope is comprised of a stage on which a specimen is placed, an illuminating optical system for supplying an illuminating light beam for illuminating the specimen placed on the stage toward the specimen, and an observation optical system for observing therethrough the specimen illuminated by the illuminating optical system. In such a microscope, the image of the specimen placed on the stage is observed through an objective lens. Accordingly, the range of the image which can be observed at any given time by means of the objective lens is remarkably limited.
Also, a Koehler illuminating optical system for uniformly illuminating the specimen is widely used as the illuminating optical system of such a microscope. In this Koehler illuminating optical system, when an objective lens is interchanged, the observation field on the specimen changes and therefore, it is necessary to regulate the range of illumination in conformity with the interchange of the objective lens. In the regulation of the range of illumination for that purpose, where use is made of an objective lens of relatively high magnification (e.g. four or more times), the change of the observation field can be accommodated by regulating a field stop or an aperture stop without changing a lens constituting the Koehler illuminating optical system. In contrast, where use is made of an objective lens of relatively low magnification (e.g. smaller than four times), the change of the observation field cannot be accommodated unless the condenser lens of the illuminating optical system is interchanged.
In recent years, the improved chromatic reproducibility and resolving power of television cameras have given rise to increased opportunities to use television cameras for microscopic observation. In such microscopic observation using a television camera, the image of a specimen formed on the imaging plane of an objective lens is further enlarged by a zoom lens and the enlarged image of the specimen is picked up by the television camera, and is displayed on a display device for observation. In the case of an ordinary microscope, the change of observation magnification is effected by the interchange of an objective lens, while in the case of microscopic observation using a television camera and a zoom lens in this manner, the change of observation magnification can be accomplished both by interchanging the objective lens and changing the zoom ratio of the zoom lens. However, again in such a microscope provided with a zoom lens, the specimen is observed through an objective lens and therefore, the range of the specimen which can be observed at any given time is limited. Also, where observation is done by the use of an objective lens of low magnification (smaller than four times), it is necessary to interchange a condenser lens for regulation as in the other prior-art microscopes, and this has been very cumbersome.